stratification是什么意思

　　Stratification in polar water normally is weak and transient.

　　极地水域的成层性是微弱而暂时的`。

　　Stratification in polar waters normally is weak and transient.

　　极地水域的成层性是微弱而暂时的。

　　The stratification of beach deposits has been studied particularly.

　　对海滩沉积物的层理进行了着重研究。